The present invention relates to combustion chambers and more particularly to any type combustion chamber for a gas turbine engine, the construction of the combustion chamber being such that the fuel-air mixture is combusted in such a manner that the formation of carbon, and hence visible smoke emission is markedly reduced. This smoke reduction is accomplished while maintaining all other combustion chamber performance parameters, such as combustion efficiency, combustion stability, altitude ignition, and durability.
As background, it is well known that a combustion chamber for use in a gas turbine must possess certain characteristics in order to satisfactorily perform its function, and this is particularly true of a gas turbine engine employed in a jet aircraft. The combustion chamber must be capable of easy startup at ground level through a range of ambient air temperatures representing cold and hot weather conditions, that is, low fuel flows and short ignition delay time so as not to result in an explosive or hot start. In the case of a can-annular type burner which will be the type burner primarily discussed herein, after ignition of the fuel-air mixture in the burners that are equipped with spark igniters or some other ignition source, the flame must propagate to adjacent burners for a full lightoff and then accelerate to idle speed. The combustor must also have the capability of good stability limits, that is, operate satisfactorily at fuel-air ratios below and above the normal idle and rated thrust fuel-air ratios in order to insure that during transient conditions, such as acceleration and deceleration operational modes which can result in off-design fuel-air ratio levels, the burners will not flame out. An additional characteristic that the combustion chamber must have is that it must be capable of altitude ignition over a wide flight speed and altitude range without causing compressor stall or other penalties which would prevent the engine from being brought up to idle speed. Additionally, the combustion chamber, after reaching idle speed, must have the capability of being accelerated to higher power settings, and this must be accomplished in a relatively short time, normally within seconds. The combustion chamber must also have the capability of producing a satisfactory discharge temperature pattern or be capable of alteration to result in such a pattern without detrimental effect of the previously mentioned performance parameters, in order to achieve long life of parts receiving the hot discharge gases from the burner. Finally, the combustion chamber must provide an atmosphere of combustion wherein the fuel-air mixture when combusted does not result in the emission of visible smoke from the engine.
While many of the elements employed in the present invention are described in the prior art, for example, the Johnson patent, U.S. Pat. No. 3,134,229, the Schiefer patent, U.S. Pat. No. 2,974,485, the Panko patent, U.S. Pat. No. 3,352,106 and the Bachle patent, U.S. Pat. No. 3,018,625, it is pointed out that none of these particular references or the prior art in general solves the particular problem as the present invention does. As hereinbefore noted, in order to provide an acceptable combustion chamber for use in a gas turbine engine, it is necessary to maintain the performance parameters hereinbefore mentioned. Smoke emission has been a problem which the prior art combustion chamber constructions have accepted so as not to penalize or adversely affect these performance parameters. The present invention does not accept smoke emission and substantially eliminates smoke emission without any penalty to the performance parameters hereinbefore mentioned.